根瘤共生对紫花苜蓿抗寒性的影响

以保定紫花苜蓿（Medicago sativa L.‘Baoding’）幼苗为试验材料，分别进行接种根瘤菌处理并确认结瘤固氮（activated-nodules，AN）和不接种根瘤菌处理（non-nodules，NN）。将生长120 d的植株放在-6℃培养箱低温胁迫12 h。通过测定叶片电导率、丙二醛MDA、渗透势、过氧化氢H₂O₂、超氧阴离子自由基O₂^·-、还原性谷胱甘肽GSH、抗坏血酸VC、叶绿素a、叶绿素b、叶绿素总量等10个指标，研究根瘤共生对紫花苜蓿抗寒性的影响。结果表明：与不接种根瘤菌苜蓿相比，低温胁迫导致根瘤固氮苜蓿较轻的细胞膜损伤和氧化损伤，并且根瘤固氮苜蓿在低温胁迫中叶绿素破坏较不接种根瘤菌苜蓿缓慢，说明根瘤与紫花苜蓿共生可以提高苜蓿抗寒性。

Effect of Root Nodules on Cold Resistance of Alfalfa (Medicago sativa)

Alfalfa (Medicago sativa L. ‘Baoding’) seedlings were exposed to be inoculated rhizobium (activated-nodules, AN) and non-inoculated rhizobia (non-nodules, NN), respectively. The 120-day seedlings were subjected to cold stress (-6℃) for 12 hours. The physiological changes were analyzed including leaf electrical conductivity, methane dicarboxylic aldehyde (MDA), leaf osmotic potential, hydrogen peroxide (H₂O₂), superoxide anion radical (O₂^·-), reduced glutathione (GSH), Vitamin C (VC), chlorophyll a, b and total chlorophyll content. Results showed that compared with alfalfa without nodules, alfalfa with activated nodules had lower cell membrane and oxidative damage when they were exposed to cold stress. Moreover, chlorophyll in AN decreased more slowly under cold stress than that in NN. These results indicate that rhizobia and alfalfa symbiotic interaction could improve alfalfa cold tolerance.